Older homes in the M Streets often have roof systems that are very different from what we see on newer construction. This roof near Mockingbird Elementary School inDallas 75206 was a good example.
The existing roof had traditional three-tab asphalt shingles over older plank decking. As part of an insurance roof replacement, we upgraded the house to an Owens Corning dimensional shingle in Driftwood and installed new 1/2-inch OSB decking over the existing wood planks.
The result was both a better-looking roof and a much better surface for installing the new shingles.
Upgrading From Three-Tab to Dimensional Shingles
The original roof was a traditional three-tab shingle, which was once extremely common throughout East Dallas. The inspection photographs show the flatter, more uniform appearance typical of an older three-tab roof.
For the replacement, the homeowner upgraded to an Owens Corning dimensional shingle in Driftwood. The dimensional shingle has more variation in thickness, shadow lines and color than the old three-tab roof, which works particularly well with the architecture of many older M Streets homes. The project invoice confirms the Owens Corning Driftwood material.
This wasn’t a dramatic architectural change. It was simply an upgrade that gave the house a more finished appearance while replacing an older roofing system.
The Bigger Issue Was Underneath the Shingles
One of the more interesting parts of this roof wasn’t the shingles at all. It was the roof decking underneath them.
Like many older homes in this part of Dallas, the house had individual wood planks rather than modern 4x8 sheets of plywood or OSB. The attic photograph from the original inspection clearly shows the older plank roof deck.
These are commonly 1x8 or 1x10 boards installed across the rafters. This was a normal way to build a roof decades ago and there is usually no reason to remove sound planking simply because it is old.
There can, however, be a problem with installing today’s asphalt shingles directly over it.
Wood moves as it ages. Individual boards can shrink, cup and curl. Gaps between the boards can also become larger over time. The result is a roof deck that isn’t as flat or consistent as a modern sheet deck.
On this house, we left the existing plank decking in place and installed 1/2-inch OSB over it before installing the new roofing system.
That creates a continuous, uniform nailing surface without unnecessarily tearing out the original roof deck.
Why Overlay the Existing Plank Deck?
Removing all of the original 1x planking usually isn’t necessary when the existing wood remains structurally sound.
Overlaying it with OSB accomplishes several things.
It gives the shingles a flatter surface. It provides a consistent location for roofing nails. It eliminates many of the problems created by gaps between individual boards. It also helps prevent irregularities in old plank decking from showing through the finished roof.
The original boards still contribute to the roof structure. The OSB simply creates a better surface for the modern roofing system installed above them.
This approach is fairly common when replacing roofs on older homes in East Dallas.
An Older Part of Dallas
This section of the M Streets is close to Mockingbird Elementary School and not far from the site of the old Dr Pepper bottling plant.
That plant was once a recognizable part of this section of Dallas but is now gone, while many of the surrounding houses remain. Those older homes are one reason we regularly encounter construction details such as plank roof decking in neighborhoods around Lower Greenville and the M Streets.
The houses may have been remodeled several times above the roofline, but underneath the shingles we often find much of the original construction still in place.
Finished Roof
Once the 1/2-inch OSB overlay was installed, the new Owens Corning dimensional shingles could be installed over a flat and consistent roof deck.
The finished photographs show a substantial visual difference from the original three-tab roof. The Driftwood dimensional shingle adds considerably more depth and variation while still looking appropriate on an older East Dallas home.
For this project, the upgrade wasn’t simply changing one shingle for another. Correcting the roof deck underneath the shingles was an important part of building the new roof correctly.
Frequently Asked Questions About Roofing Over Old 1x8 and 1x10 Plank Decking
Should you install a new asphalt shingle roof directly over old 1x8 or 1x10 boards?
Usually not if the existing plank deck has significant gaps, cupping or other irregularities.
Older plank decking can move considerably over its lifetime. Installing asphalt shingles directly over an uneven deck can affect both the appearance of the roof and the consistency of the nailing surface.
The condition and spacing of the existing boards should be evaluated before the new roof is installed.
Can the old 1x8 or 1x10 roof decking stay in place?
Yes.
If the existing boards are structurally sound, they generally do not need to be removed simply because the roof is being converted to a sheeted deck.
A common solution is to leave the original boards in place and install plywood or OSB over them.
On this M Streets roof, we installed 1/2-inch OSB over the existing plank decking.
Why aren’t old 1x8 or 1x10 boards always a good surface for modern shingles?
Individual boards can shrink, cup and curl as they age.
That can create uneven areas in the roof deck, along with gaps where roofing nails may not have a solid wood substrate underneath them. Irregularities in the decking can also become visible through the finished shingles.
Adding sheet decking creates a much more consistent surface.
Is it better to remove the old boards or install OSB over them?
If the original boards are structurally sound, removing all of them is often unnecessary.
Installing OSB or plywood over the existing deck preserves the original roof structure while providing the smooth, continuous surface needed for a modern asphalt shingle roof.
Damaged or deteriorated boards should still be repaired or replaced as needed before the new decking is installed.
Does adding OSB over plank decking strengthen the roof?
It can make the roof deck considerably more uniform and rigid, but that isn’t the primary reason for doing it.
The main objective is to create a continuous, dependable substrate for the roofing system. The result is a flatter deck, more consistent fastening and a better installation surface for the new shingles.
